Method and device for determining an operational geographical zone observed by a sensor

ABSTRACT

The method serves to determine an operational geographical zone (ZO) relative to a sensor (S) configured to observe and measure the radial speed of an object traveling with a non-zero minimum speed “VT” in a region of interest (ROI). The method comprises:
         a step of simulating the position of said sensor (S);   a step of determining a first zone (A 1 ) of the region of interest constituted by points at each of which said object at that point traveling at a speed greater than or equal to said speed VT and in a given direction “DT”, would be seen by said sensor (S) as having a radial speed greater than a threshold speed defined for that point; and   the operational geographical zone (ZO) being defined by taking account of the intersection of the first zone (A 1 ) and of a coverage zone (A 2 ) of the sensor.

BACKGROUND OF THE INVENTION

The present invention relates to a method and to a device for assistingin placing a sensor, e.g. a Doppler radar.

In the present state of the art, a widespread approach for placing aDoppler radar consists in superposing a coverage zone of the radar on abackground map showing the surveillance zone.

The positioning is performed by the operator taking account of thecharacteristics of the site (presence of obstacles, possibilities forinstallation), of operational needs (coverage of zones that areparticularly sensitive), and of characteristics of the radar (variationsin detection performance between the core and the ends of the coveragezone of the radar).

The invention seeks a method for facilitating the positioning of aDoppler radar, and more generally of a sensor.

OBJECT AND SUMMARY OF THE INVENTION

Thus, in a first aspect, the invention provides a determination methodfor determining at least one operational geographical zone in a regionof interest, said zone being determined relative to a sensor configuredto observe and measure the radial speed of an object traveling at anon-zero minimum speed “VT” in the region of interest. The methodcomprises:

-   -   a step of simulating the position of the sensor in the region of        interest at a position and in an orientation that are        determined;    -   a step of determining at least one first zone of the region of        interest that is constituted by points for each of which, the        object at that point and traveling at a speed greater than or        equal to the speed VT and in at least one given direction “DT”,        would be seen from the sensor to have a radial speed greater        than a threshold value defined for that point; and    -   a step of determining a second zone of the region of interest,        the second zone constituting a coverage zone of the sensor in        which said object is observable while taking account at least of        the intrinsic characteristics of the sensor and of the intrinsic        characteristics of the object, and also of the position of the        object relative to the sensor;

the operational geographical zone being defined by taking account of theintersection of at least these two zones.

Thus, and in general manner, the invention proposes determining thepositions of the sensor at which an object traveling at a speed greaterthan or equal to a given speed VT and in a given direction DT is visibleto the sensor. This zone is referred to as an “operational zone” in themeaning of the invention.

The operational zone is thus defined by the intersection of at least twozones, namely:

-   -   a first zone defined essentially as a function of sensitivity of        the sensor defined for the various points of the region of        interest in terms of speed threshold, without taking account of        the orientation of the sensor;

and

-   -   the coverage zone of the sensor defined as a function of the        intrinsic characteristics of the sensor, of the intrinsic        characteristics of the object to be observed, and, except in the        special situation of a sensor with an isotropic antenna, of the        orientation of the sensor.

In an embodiment of the invention, the sensor is a Doppler radar.

Determining settings for the determination method of the inventionconsists in determining the sensitivity of the sensor by setting speedthresholds at the various points in the region of interest.

More precisely, the greater the desire to be able to detect objects at agiven point in the region of interest, the lower the threshold speed atthat point needs to be selected. The sensitivity of the sensor is saidto be “high” since numerous objects (e.g. the leaves of a tree stirredby the wind) become visible to the sensor.

Conversely, by increasing the speed threshold at a point, thesensitivity of the sensor is reduced, which can be advantageous foravoiding false positives.

In an implementation, the method includes a step of displaying theposition of the sensor, together with the first zone and the second zonein the region of interest, e.g. on a computer screen.

This display makes it easy for an operator to verify whether a positionof the sensor makes it possible to carry out effective surveillance of aportion of the region of interest against intrusions of an objecttraveling at some given minimum speed and in a given direction. Theoperator can also evaluate the extent to which the sensitivityadjustment of the sensor at various different points has an impact onthe effectiveness of the method in carrying out surveillance of aportion of the region of interest.

Optionally, shadow zones and interference zones may also be shown.

In an implementation of the invention, the threshold speeds defined atall of the points of the region of interest are equal to a constant. Inthis implementation, the first zone presents the simple shape of twoangular sectors that meet at their vertices, which correspond to theposition of the sensor, and that have a bisector corresponding to thegiven direction, with an aperture that is determined by the sensitivityof the sensor, in other words the constant threshold speed in the regionof interest.

It should be observed that this first zone is not oriented as a functionof the antenna pattern of the sensor, but by the direction of theintrusion path.

This implementation presents the advantage of being able to use a simplesensor that need not supply the bearings nor the distances of objectsthat are detected. It can be implemented using an unmodulated continuouswave Doppler radar having an antenna constituted by a simple dipole.

Compared with continuous wave radars with modulated transmission, thistype of radar presents the advantage of needing a processing system thatis simpler. Since it no longer needs to provide the bearing, the designof the antenna and of its processing system can be greatly simplified.

An antenna constituted by a simple dipole is particularly compact andsimple compared with an antenna that gives a bearing measurement bymaking use of mechanical scanning, or relative to an antenna made up ofa plurality of mutually spaced-apart dipoles and measuring the phasedifferences of the signals they receive, which requires additionalprocessing that is unnecessary in this implementation.

Because of its geometry, the first zone may be referred to as a “Dopplerrose” by a person skilled in the art of radars or of aerial navigation.

In a particular implementation, the threshold speed defined for at leastone point of said region of interest is defined as a function of theposition of that point relative to said sensor.

This implementation thus makes it possible to adjust the sensitivity ofthe sensor at different points in the region of interest. It isparticularly advantageous when the region of interest has a plurality ofzones presenting uniform characteristics. For example, if the region ofinterest has an unobstructed zone where the risk of detecting falsepositives is low, it may be advantageous to increase sensitivity in thiszone, in other words to lower the threshold speed for points in thatzone in order to increase the chances of detection.

For example, the threshold speed defined for at least one point of theregion of interest is defined as a function of the distance between thatpoint and the sensor.

This implementation is particularly advantageous in that, while stillusing a sensor that is simple and that does not require bearing to bemeasured, it is capable of satisfying a need to install the sensor in anunobstructed zone that is surrounded by zones of vegetation. It is thuspossible to increase the sensitivity in the unobstructed zone close tothe sensor, in other words to lower the threshold speed for points inthat zone in order to increase the chances of detection, while alsoreducing sensitivity, in other words increasing the threshold speed, forpoints situated outside the unobstructed zone. A sensor in which thethreshold speed cannot be defined as a function of distance must eitherreduce its sensitivity, in other words increase the threshold speed overthe entire region of interest in order to avoid false positives, orelse, where the sensor makes this possible, it must increase itssensitivity while limiting the range of the sensor to the unobstructedzone.

In an implementation, the threshold speed defined for at least one pointof the region of interest is defined as a function of the bearing ofthat point relative to the reference direction linked to the sensor,e.g. the axis of the main lobe for a sonar or a radar having adirectional antenna. This implementation can be envisaged only if thesensor can measure the bearings of the points that it observes.

On this topic, prior art FIG. 1 illustrates a known example of anantenna having a transmitter TX and two receivers RX1 and RX2 that arespaced apart from each other, and that are situated at respectivedistances d1 and d2 from an object T in order to measure the bearing θof the object T by a phase monopulse as described in detail in thearticle “Doppler and direction-of-arrival (DDOA) radar formultiple-mover sensing” (dol:10.1109/TAES.2007.4441754) published in thejournal IEEE Transactions on Aerospace and Electronic Systems, Vol. 43,No. 4, October 2007, page 1497.

For example, if the sensor is positioned at the end of an asphalt roadpassing through a wooded zone, it may be advantageous to increase thesensitivity of the sensor for points on that road, in other words forpoints in the region of interest at a bearing, as seen from the sensor,that corresponds to the direction of that road.

In a particular implementation, the threshold speed defined for at leastone point of the region of interest is defined as a function of theelevation of that point relative to said sensor.

With reference to FIG. 2, this implementation serves for example to beable to increase the sensitivity of the sensor, e.g. to lower thethreshold speed, for a first zone A1 without foliage as defined by anangle of elevation less than a value φ0, e.g. in order to observeobjects flying at very low radial speed, such as drones.

When the threshold speed defined for a point of the region of interestvaries as a function of the distance, of the bearing, and/or of theelevation of that point relative to the sensor, the geometry of thefirst zone may be of arbitrary shape.

In accordance with the invention, the first zone is defined for a giventravel direction of the object. If the invention is used to position asensor in order to provide surveillance of a straight fence CR as shownin FIG. 3, this direction DT is preferably selected to be in thepreferred direction for crossing the fence, i.e. substantiallyperpendicular to the fence, regardless of the position or theorientation of the sensor S.

In a particular implementation, the method of the invention makes itpossible to determine a plurality of first zones for the same travelspeed VT of the object, these first zones being determined for differenttravel directions of the object. As shown in FIG. 4A, thisimplementation of the invention can be used advantageously to performsurveillance of an angled fence CA made up of two non-parallel straightportions, the travel directions DT1 and DT2 of the object being selectedto be substantially perpendicular to each of those two portions.

In the particular implementation shown in FIG. 4A, the first zones A1.1and A1.2 obtained for each of the travel directions DT1 and DT2 of theobject are shown in different manners, e.g. using different colors ordifferent patterns.

By taking the example of two first zones, the person skilled in the artcan understand that the operational zones in the meaning of theinvention, i.e. the zones in which an object traveling at a speedgreater than or equal to a given speed VT and in one or the other of thegiven directions DT is visible to the sensor, are the zones that areobtained respectively by the intersection between the first zone A1-1and the second zone A2 and also by the intersection between the firstzone A1-2 and the second zone A2, as shown respectively in FIGS. 4B and4C. These figures show that the intersection zone obtained for thesensor as positioned in this way overlap respectively the fence portionCR1 for the detection DT1 and the fence portion CR2 for the detectionDT2.

When for practical reasons the sensor can be positioned at a positionthat makes it possible to define such an intersection zone that coversthe region that is to be protected effectively, the operator looks for aposition for the sensor that gives optimized coverage, either by trialand error, or else by performing a method in accordance with theinvention for assisting in installing a sensor.

Specifically, in a second aspect, the invention provides a method ofassisting in installing a sensor configured to observe and measure aradial speed of an object traveling at a non-zero minimum speed “VT” andin at least one given direction “DT” in a region of interest, the methodcomprising:

-   -   at least one iteration, each iteration comprising determining an        operational geographical zone of the sensor by simulating the        sensor being positioned in the region of interest at a        determined position and in a determined orientation, by        performing an above-mentioned method of determining such a zone;    -   a step of determining at least one preferred position among the        positions enabling an optimized operational geographical zone to        be determined in accordance with an optimization criterion; and    -   a step of reproducing this or these preferred position(s).

The invention thus proposes a method making it possible to optimizeautomatically the position of the sensor as a function of apredetermined optimization criterion. By way of example, theoptimization criterion may serve to obtain the widest geographical zone,while possibly complying with other constraints, such as for example theconstraint of necessarily being able to cover a defined zone in theregion of interest.

In accordance with the invention, the operational zone is obtained fromthe intersection of the first zone(s) and the second zone in the meaningof the invention.

In implementations of the method of the invention for providingassistance in installing a sensor, and as shown in FIG. 5, theoperational zone ZO takes account of the intersection between the firstzone(s) and the second zone (respectively A1 and A2) with the complementof at least one shadow zone A3, this at least one shadow zone takingaccount of characteristics in said region of interest. This shadow zoneis typically constituted by points in the region of interest thatcorrespond to positions at which the object cannot be observed by thesensor S while the sensor is in its simulated position, e.g. because ofthe presence of a building B.

By way of example, and as shown in FIG. 6, a shadow zone A3 may beconstituted by a zone that seen from the sensor S is situated behind arelief or an obstacle OBS, such that an object T positioned in this zonecannot be observed by the sensor. In this figure, the angle formedbetween the travel direction DT of the object and the straight lineconnecting the target to the sensor is marked β.

In a variant, the shadow zone is not taken into account when calculatingthe operational zone, however it is shown to the user.

In implementations of the invention, the determination method of theinvention also includes a step of determining an interference zone fortaking account of characteristics in said region of interest. This zonemay typically be constituted by points in the region of interest thatcorrespond to positions where said object might not be detected by thesensor so long as it is in its simulation position.

By way of example, such an interference zone may be constituted by abusy road. It may be shown to the user with a representation that isdifferent from the representations used for showing the first and secondzones, and the shadow zones, if any.

The invention also provides a device for determining at least oneoperational geographical zone in a region of interest, the zone beingdetermined relative to a sensor configured to observe and measure theradial speed of an object traveling at a non-zero minimum speed “VT” inthe region of interest. The device comprises:

-   -   a unit for simulating the sensor being positioned in the region        of interest at a determined position and in a determined        orientation;    -   a unit for determining at least one first zone of the region of        interest that is constituted by points at each of which, the        object at that point and traveling at a speed greater than or        equal to the speed VT and in a given direction “DT”, would be        seen by the sensor to have a radial speed greater than a        threshold speed defined for that point; and    -   a unit for determining a second zone of the region of interest,        the second zone constituting a coverage zone of the sensor in        which the object is observable while taking account at least of        the intrinsic characteristics of the sensor and of the intrinsic        characteristics of the object, and also of the position of the        object relative to the sensor;

the operational geographical zone being defined by taking account of theintersection of at least the first and second zones.

The invention also provides a device for assisting installing a sensorthat is configured to observe and measure the radial speed of an objecttraveling at a non-zero minimum speed “VT” and in at least one givendirection “DT” in a region of interest. The device comprises:

-   -   a controller configured to execute at least one iteration, each        iteration comprising determining an operational geographical        zone of the sensor by simulating the sensor being positioned in        the region at a determined position and in a determined        orientation, by implementing an above-mentioned method of        determining such a zone;    -   a unit for determining at least one preferred position from        among the positions enabling an optimized operational        geographical zone to be determined in accordance with an        optimization criterion; and    -   a unit for representing the preferred position(s).

In a particular implementation, the various steps of the method ofdetermining an operational geographical zone and/or the method ofassisting in installing a sensor, as mentioned above, are determined bycomputer program instructions.

Consequently, the invention also provides a computer program on a datamedium, the program including instructions adapted to performing stepsof a method of determining an operational geographical zone and/or amethod of assisting in installing a sensor, as mentioned above.

The program may use any programming language, and be in the form ofsource code, object code, or code intermediate between source code andobject code, such as in a partially compiled form, or in any otherdesirable form.

The invention also provides a computer-readable data medium includinginstructions of a computer program as mentioned above.

The data medium may be any entity or device capable of storing theprogram. For example, the medium may comprise storage means, such as aread only memory (ROM), e.g. a compact disk (CD) ROM, or amicroelectronic circuit ROM, or indeed magnetic recording means, e.g. ahard disk.

Furthermore, the data medium may be a transmissible medium such as anelectrical or optical signal, suitable for being conveyed via anelectrical or optical cable, by radio, or by other means. The program ofthe invention may in particular be downloaded from an Internet typenetwork.

Alternatively, the data medium may be an integrated circuit in which theprogram is incorporated, the circuit being adapted to execute or to beused in the execution of the method in question.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1, described above, shows the prior art with an antenna suitablefor measuring the bearing of an object;

FIG. 2, described above, shows a first high-sensitivity zone forelevation angles corresponding to a zone without foliage;

FIG. 3, described above, shows a first zone for a given travel directionof the object;

FIG. 4A, described above, shows the second zone and two first zones fortwo given travel directions of the object;

FIGS. 4B and 4C, described above, show the operational zones obtainedfor two given travel directions of the object;

FIG. 5, described above, shows an operational zone defined by taking ashadow zone into account;

FIG. 6, described above, shows a shadow zone;

FIG. 7 is a diagram of a device for assisting in installing a sensor inaccordance with a particular embodiment of the invention;

FIG. 8 is a flow chart showing the main steps of a method of assistingin installing a sensor in accordance with a particular implementation ofthe invention;

FIG. 9 shows the display on the screen of the FIG. 7 device, showing aregion of interest, a surveillance zone, and a travel direction of anobject;

FIG. 10 shows a radial speed calculation;

FIG. 11 shows a first zone for a given travel direction of the object;

FIG. 12 shows two resulting first zones for two travel speeds of anobject;

FIG. 13 shows the resultant of a plurality of first zones of arbitraryshapes;

FIG. 14 shows an example of a coverage zone of the sensor for a givenobject;

FIGS. 15A to 15C show an example of determining an interference zone ina particular implementation of the invention;

FIG. 16 shows an interference zone in another particular implementationof the invention;

FIG. 17 shows an example of a surveillance zone and of an operationalzone; and

FIG. 18 shows a computer screen, a sensor, a surveillance zone, a firstzone, a second zone, and an operational zone.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

There follows a detailed description of non-limiting embodiments of theinvention.

FIG. 7 is a diagram showing a device 10 for assisting in installing asensor in accordance with a particular embodiment of the invention. Inthis particular embodiment, the device has the conventional architectureof a computer. In particular, it comprises a processor 11, a ROM 12, arandom access memory (RAM) 13, a keyboard 14, a mouse 15, and a screen16. The device may be connected to a sensor 17.

In the presently-described embodiment, only one sensor is used, whichsensor comprises a single-lobe anisotropic antenna.

In an alternative embodiment, the device 10 does not use a keyboard or amouse, but rather a touch screen that serves both to input informationand to display it. In this embodiment, the device 10 may be constitutedby a smartphone or a touch tablet, possibly connected to a server.

The ROM 12 constitutes a data medium in accordance with the invention.It stores a computer program PG in accordance with the invention. Thecomputer program PG includes instructions for executing steps of amethod of assisting in installing a sensor in accordance with animplementation of the invention, with the main steps of the method beingdescribed below with reference to FIG. 8.

In the presently-described embodiment, the ROM 12 of the computer alsoincludes a digital map showing a region of interest ROI including asurveillance zone ZS. This digital map may be displayed on the screen 16of the computer.

The keyboard 14 and the mouse 15 may be used by the operator to inputconfiguration settings for the method of assisting installation, e.g.:

-   -   the perimeters of the region of interest ROI and of the        surveillance zone ZS;    -   Optionally, the obstacles and the relief in the region of        interest ROI serve to calculate potential shadow zones;    -   the characteristics of the object T to be observed, e.g. a        person, a type of vehicle, . . . ;    -   a minimum travel speed VT of the object;    -   one or more travel directions DT of the object;    -   threshold speeds V min_i at the various points Ti of the region        of interest ROI;    -   an optimization criterion for installing the sensor;    -   an option enabling the operator to take account of potential        shadow zones while determining the operational zone of the        sensor;    -   optionally the characteristics and the locations of sources of        interference, serving in particular to determine potential zones        of interference; and    -   the position POS and the orientation γ of the sensor, in the        “manual” mode of operation as described below.

These settings may be saved in the ROM 12.

FIG. 9 shows the display on the screen 16 of a region of interest ROI,of a surveillance zone ZS, and of a travel direction DT of an object.

In the presently-described embodiment, the man/machine interface of thecomputer 10 provides the user with two modes of operation:

-   -   in a so-called “manual” mode, the operator selects a position        POS for the sensor S, and if the sensor is anisotropic, an        orientation γ, e.g. by clicking with the mouse on the digital        map, and the computer program PG determines and displays on the        screen 16 the operational zone of the sensor S when in this        position POS for the speed VT and the travel direction(s) of the        object T; and    -   in a so-called “automatic” mode, the computer program calculates        and displays to the operator on the screen 16 one or more        preferred positions and/or orientations for the sensor in order        to optimize the geographical zone, which zone is optimized in        compliance with an optimization criterion.

In general manner, and as mentioned above, the operational zone Zcorresponds to the positions in which an object is visible to the sensorand is defined by the intersection between at least one first zone A1and a zone A2, which zones are described in greater detail below.

Concerning the First Zone A1

It should be recalled that a point Ti of the region of interest ROIbelongs to the first zone A1 if, and only if, an object at the point Titraveling at a given speed VT and in a given direction DT has, when seenfrom the sensor S, a radial speed Vr that is greater than a thresholdspeed V min_i defined for that point.

FIG. 10 illustrates these concepts. It shows a sensor S positioned in aregion of interest ROI and an object T traveling in this region at aspeed VT in a direction DT. The radial component (or radial speed) Vr ofthis object T forms an angle α with the direction DT, such that:

Vr=VT·cos α

when the direction DT, the sensor, and the object are all situated inthe horizontal plane.

In the general situation, if the angle formed between the direction DTand the straight line connecting the target to the sensor is written β,as shown in FIG. 6, then:

Vr=VT×cos α×cos β

FIG. 11 shows such a first zone A1 shaded for when the threshold speedsV min_i associated with the various points in the region of interest ROIare all equal to the same constant V min.

This first zone A1 in this implementation is in the form of two angularsectors:

-   -   that meet at their vertices at a position corresponding to the        position of the sensor S;    -   of bisector corresponding to the direction DT; and    -   of aperture 2α₀ associated with the sensitivity V min of the        sensor, where:

α₀=arccos(V min/VT)

In other words, at constant speed VT, the more it is desired to be ableto detect objects, the lower the value that needs to be given to thethreshold speed V min, such that α₀ tends towards π/2. In thisimplementation, the sensitivity of the Doppler sensor is said to behigh, since numerous objects (e.g. vegetation stirred by the wind)become visible to the sensor.

Conversely, at constant speed VT, with decreasing sensitivity of theDoppler sensor (V min close to VT), then α₀ tends towards 0.

Because of this particular geometry, the first zone A1 may be referredto by a person skilled in the art of radars or of aerial navigation as a“Doppler rose.”

With reference to FIG. 12 there can be seen the first zone A1 in anexample in which the speed V min_i associated with a point Ti of theregion of interest ROI depends on the distance between that point Ti andthe sensor S, and only on that distance.

More precisely, in this figure, it is considered that:

-   -   the points Ti situated at a distance from the sensor S that is        less than a limit distance RL are associated with a first        threshold speed V min1; and    -   the points Ti situated at a distance from the sensor S that is        greater than this limit distance RL are associated with a second        threshold speed V min2.

This figure shows the situation in which the threshold speed V min1 islower than the threshold speed V min2 such that α1 is greater than α2.Such a configuration may correspond to a scenario in which thesensitivity of the sensor is increased for the zone located in theproximity of the sensor, e.g. when the sensor is positioned in a zonethat is unobstructed.

The geometry of the first zone A1 is not necessarily made up of portionsof angular sectors as shown in FIGS. 11 and 12. Specifically, withreference to FIG. 13, there is shown a first zone A1 (union of theshaded portions) that corresponds to an embodiment in which thethreshold speed V min_i associated with the points Ti of the region ofinterest ROI takes account of the distance of the point Ti from thesensor, and also its bearing angle θ.

In general manner, the shape of the first zone A1 is arbitrary, thisshape depending exclusively, for given speed VT and direction DT, solelyon the threshold values V min_i associated with the points Ti in theregion of interest ROI.

Concerning the Second Zone A2

In accordance with the invention, the second zone A2 constitutes acoverage zone of the sensor S in which the object T that is to beobserved is observable, this coverage zone being defined by takingaccount at least of the intrinsic characteristics of the sensor S, theintrinsic characteristics of the object T, and also the position of theobject T relative to the sensor S.

It should be recalled that for a radar, the coverage of the radarcorresponds to the zone in which an object of the size underconsideration can reflect sufficient energy for it to be detected. Inparticular, it is possible to calculate the received power P by usingthe radar equation known to the person skilled in the art and based onthe antenna pattern (gain in a given direction), on the distance to theobject, and on the size of the object expressed as a radar cross-section(RCS):

P=P _(t) ·G _(t) ·G _(r)·λ²·σ/((4·π)³ ·R ⁴)

with:

-   -   P_(t): transmitted power;    -   G_(t)/G_(r): transmit receive gain;    -   λ: wavelength;    -   σ: radar cross-section;    -   R: distance between the radar and the object.

With reference to FIG. 14, the person skilled in the art of radarsrecognizes that this second zone is essentially in the form of a lobe inthe particular situation in which the sensor has a directional antennaand consideration is given only to the main lobe of that antenna.

In an embodiment where the sensor is anisotropic, it possesses apreferred direction generally referred to as the “boresight”. In thissituation, which is particularly representative when the sensor is aradar, a sonar, or a lidar, the second zone A2 also takes account of theorientation of the sensor relative to the object.

Concerning the Interference Zone A4

In accordance with the invention, an interference zone A4 is constitutedby points in the region of interest that correspond to positions atwhich an object T might not be detected by a sensor S.

An interference zone is typically due to the presence of interferencesources, by way of example and as shown in FIG. 15A, to the presence ofvehicles 51 traveling along a road 50 that passes through the region ofinterest ROI and in the coverage zone A2 of a sensor used for detectinghuman intrusions. It should be observed that in this example thecoverage zone that takes account of the intrinsic characteristics ofvehicles traveling on the road is wider than the coverage zone of thesensor that takes account of the intrinsic characteristics of theobjects that it is desired to detect.

In a first example, the sensor S is configured to observe and measureonly distance and radial speed Vr. Under such circumstances, if thedistance at which the vehicles are visible lies in the range D min to Dmax, the vehicles are seen by the sensor as having the same distance andradial speed characteristics as the objects to be observed that aresituated in the range D min to D max, which objects might thus not bedetected by the sensor. The interference zone A4 is thus constituted bypoints situated in the range D min to D max, i.e. the ring centered onthe sensor S that is of inside radius D min and of outside radius D max,as shown in FIG. 15B. FIG. 15C shows the intersection between theinterference zone A4 and the coverage zone A2.

It should be observed that certain sensors suitable for measuring radialspeed are the subject of a known “folding” phenomenon that leads toobjects traveling at high radial speed being confused with objectstraveling at low radial speed.

In another example, the sensor S is a continuous wave Doppler radarconfigured to observe and measure distance, radial speed Vr, and bearingby phase difference between the signals generated by the echoes receivedfrom spaced-apart sensors, as described above with reference to FIG. 1.In that embodiment, it is possible to determine the zone of false alarmsgenerated by vehicles as showed by cross-hatching in FIG. 16.Nevertheless, each individual receiver RX1 and RX2 operates like thesensor S in FIG. 15A, such that the objects that are to be observed canalso be confused in each of those individual receivers with false alarmsgenerated by vehicles in each of the receivers, thus potentially makingbearing measurements of the azimut ineffective or erroneous.

As in the above example, the interference zone A4 in the meaning of theinvention, i.e. the zone corresponding to positions in which an objectmight not be detected by the sensor, is the masking zone defined by thering centered on the sensor S and of inside radius D min and outsideradius D max.

However, and in most advantageous manner, it is also possible in thisexample to distinguish within the interference zone, the zone of falsealarms generated by vehicles and corresponding to the location of theroad.

Representation of an Operational Zone

FIG. 17 shows in cross-hatching an operational zone ZO in animplementation of the invention.

In this example, the operational zone ZO is the intersection between thefirst zone A1 of FIG. 11 and the second zone A2 of FIG. 14.

This operational zone ZO constitutes the set of positions in which anobject traveling in the direction DT at the speed VT is visible to thesensor S.

The sensor S as positioned in this way can provide effectivesurveillance of intrusions into a surveillance zone ZS by objectstraveling at the speed VT in the direction DT, the surveillance zone ZSbeing constituted by a straight fence, as shown in this figure.

Example of a Method of Assisting Installing the Sensor S

With reference to FIG. 8, there follows a description of the main stepsof a method of providing assistance in installing a sensor in accordancewith a particular implementation of the invention.

This method comprises a loop made up of steps E10 to E50, with eachiteration of the loop serving to determine, for a different positionPOSj of the region of interest ROI, the operational geographical zoneZOj of said sensor S by simulating said sensor S being positioned atsaid position POSj.

More precisely, each iteration of the loop comprises:

-   -   a simulation step E10 for simulating positioning the sensor S in        the region of interest ROI at a position POSj with an        orientation γj. In practice, the position POSj may be selected        to occupy potential zones for positioning the sensor as        predetermined by the operator, and by shifting position by steps        of a determined size between two iterations;    -   a determination step E20 for determining a first zone A1 j for        each travel direction DT of the object T, as described above        with reference to FIGS. 11 to 13;    -   a determination step E30 for determining a second zone A2 j        corresponding to the coverage zone of the sensor S, as described        above with reference to FIG. 14;    -   optionally, depending on the option selected by the operator, a        determination step E40 for determining potential shadow zones A3        in which the object T is not detectable by the sensor when        positioned in the position POSj; and    -   a determination step E50 for determining the operational zone        ZOj by taking account of the intersection between the first        zones A1, the second zone A2, and optionally the zone that is        complementary to the shadow zones A3 in the region of interest        ROI.

The steps E10 to E50 show the main steps of a method of determining anoperational zone for the sensor S in the meaning of the invention forthe sensor in the position POSj.

In a particular embodiment, the sensor possesses characteristics thatare anisotropic. In this embodiment, the step E30 of the method ofdetermining the operational zone serves to determine a second zone A2 jkfor each orientation k of the coverage zone of the sensor S. Said methodthus has two loops, iterating on different positions POSj in the regionof interest ROI and iterating on the orientation k of the sensor.

FIG. 18 shows the screen 16 of the computer 10 for a position POSj ofthe sensor S, the surveillance zone ZS, the first zone Alj, the secondzone A2 j, and the operational zone ZOj. In this example, the first zoneA1 is truncated beyond a certain distance that is set arbitrarily.

In the presently-described implementation, once the operational zone ZOjhas been determined for all of the positions POSj of the sensor S, themethod of providing assistance in installing the sensor includes adetermination step E60 for determining at least one preferred positionPOSopt for the sensor among the positions POSj, this preferred positionserving to determine an optimized operational geographical zone ZOoptcomplying with an optimization criterion. In the presently-describedimplementation, the optimized position POSopt for the sensor is theposition that serves to maximize the area of the surveillance zone ZSthat is covered by the operational zone ZOopt obtained for the positionof the sensor.

The optimized positions POSopt for the sensor may be marked on thescreen 16 for the operator so as to enable the operator to install thesensor in that position in the region of interest.

1-18. (canceled)
 19. A determination method for determining at least oneoperational geographical zone in a region of interest, said zone beingdetermined relative to a sensor configured to observe and measure theradial speed of an object traveling at a non-zero minimum speed “VT” inthe region of interest, the method comprising: a step of simulating theposition of said sensor in said region of interest at a position and inan orientation that are determined; a step of determining at least onefirst zone of said region of interest that is constituted by points foreach of which, said object at said point and traveling at a speedgreater than or equal to said speed VT and in a given direction “DT”,would be seen from said sensor to have a radial speed greater than athreshold value defined for that point; and a step of determining asecond zone of said region of interest, the second zone constituting acoverage zone of said sensor in which said object is observable whiletaking account at least of the intrinsic characteristics of said sensorand of the intrinsic characteristics of said object, and also of theposition of said object relative to said sensor; said at least oneoperational geographical zone being defined by taking account of theintersection between at least said first and second zones.
 20. A methodaccording to claim 19, wherein said threshold speeds defined for thevarious points of the region of interest are equal to a constant.
 21. Amethod according to claim 19, wherein the threshold speed defined for atleast one point of said region of interest is defined as a function ofthe position of that point relative to said sensor.
 22. A methodaccording to claim 21, wherein the threshold speed defined for at leastone point of the region of interest is defined as a function of thedistance between that point and the sensor.
 23. A method according toclaim 21, wherein the threshold speed defined for at least one point ofthe region of interest is defined as a function of the bearing of thatpoint relative to a reference direction linked to the sensor.
 24. Amethod according to claim 21, wherein the threshold speed defined for atleast one point of the region of interest is defined as a function ofthe elevation of that point relative to said sensor.
 25. A methodaccording to claim 19, further comprising a step of determining at leastone shadow zone taking account of the characteristics of said region ofinterest, said at least one shadow zone being constituted by the pointsthat correspond to positions at which said object is not detectable bythe sensor when positioned thereat, and wherein said operationalgeographical zone is defined by taking account of the intersectionbetween the complement of at least one of said shadow zones and saidfirst and second zones.
 26. A method according to claim 19, furthercomprising a step of determining an interference zone taking account ofthe characteristics of said region of interest, said interference zonebeing constituted by points corresponding to positions at which saidobjects might not be detected by the sensor when positioned at saidposition.
 27. A method according to claim 19, characterized in that itcomprises determining a plurality of said first zones, said first zonesbeing determined for different travel directions of said object.
 28. Amethod according to claim 19, comprising a set of representing theposition of said sensor, of said at least one first zone, of said secondzone, and optionally of said shadow zone and/or of said interferencezone in said region of interest.
 29. A method according to claim 27,wherein the first zones obtained for each of said directions arerepresented in different manners.
 30. A method according to claim 19,wherein said sensor is a Doppler radar.
 31. A method of assisting ininstalling a sensor configured to observe and measure a radial speed ofan object traveling at a non-zero minimum speed “VT” and in at least onegiven direction “DT” in a region of interest, the method comprising: atleast one iteration, each iteration comprising determining anoperational geographical zone of said sensor by simulating said sensorbeing positioned in said region of interest at a determined position andin a determined orientation, by performing a method of determining sucha zone in accordance with claim 1; a step of determining at least onepreferred position among said positions enabling an optimizedoperational geographical zone to be determined in accordance with anoptimization criterion; and a step of reproducing said at least onepreferred position.
 32. A device for determining at least oneoperational geographical zone in a region of interest, said zone beingdetermined relative to a sensor configured to observe and measure theradial speed of an object traveling at a non-zero minimum speed “VT” inthe region of interest, the device comprising: a unit for simulatingsaid sensor being positioned in said region of interest at a determinedposition and in a determined orientation; a unit for determining atleast one first zone of said region of interest that is constituted bypoints at each of which, said object at said point and traveling at aspeed greater than or equal to said speed VT and in a given direction“DT”, would be seen by said sensor to have a radial speed greater than athreshold speed defined for that point; and a unit for determining asecond zone of said region of interest, the second zone constituting acoverage zone of said sensor in which said object is observable whiletaking account at least of the intrinsic characteristics of said sensorand of the intrinsic characteristics of said object, and also of theposition of said object relative to said sensor; said at least oneoperational geographical zone being defined by taking account of theintersection of at least said first and second zones.
 33. A device forassisting installing a sensor that is configured to observe and measurethe radial speed of an object traveling at a non-zero minimum speed “VT”and in at least one given direction “DT” in a region of interest, thedevice comprising: a controller configured to execute at least oneiteration, each iteration comprising determining an operationalgeographical zone of said sensor by simulating said sensor beingpositioned in said region at a determined position and in a determinedorientation, by implementing a method of determining such a zone inaccordance with claim 19; a unit for determining at least one preferredposition from among said positions enabling an optimized operationalgeographical zone to be determined in accordance with an optimizationcriterion; and a unit for representing said at least one preferredposition.
 34. A computer program including instructions for executingsteps of the determination method according to claim 19 when saidprogram is executed by a computer.
 35. A computer program includinginstructions for executing steps of the method according to claim 31 forassisting in installing a sensor, when said program is executed by acomputer.
 36. A computer readable data medium including instructions ofa computer program enabling steps of a determination method according toclaim 19 to be executed, and/or including instructions of a computerprogram enabling steps of a method according to claim 31 for assistingin installing a sensor.